The invention relates to the isolation, characterization and utilization of the causative agent of the Mystery Swine Disease (MSD). The invention utilizes the discovery of the agent causing the disease and the determination of its genome organization, the genomic nucleotide sequence and the proteins encoded by the genome, for providing protection against and diagnosis of infections, in particular, protection against and diagnosis of MSD infections, and for providing vaccine compositions and diagnostic kits, either for use with MSD or with other pathogen-caused diseases.
In the winter and early spring of 1991, the Dutch pig industry was struck by a sudden outbreak of a new disease among breeding sows. Most sows showed anorexia, some aborted late in gestation (around day 110), showed stillbirths or gave birth to mummified fetuses and some had fever. Occasionally, sows with bluish ears were found, therefore, the disease was commonly named xe2x80x9cAbortus Blauwxe2x80x9d. The disease in the sows was often accompanied by respiratory distress and death of their young piglets and often by respiratory disease and growth retardation of older piglets and fattening pigs.
The cause of this epizootic was not known, but the symptoms resembled those of a similar disease occurring in Germany since late 1990, and resembled those of the so-called xe2x80x9cMystery Swine Diseasexe2x80x9d as seen since 1987 in the mid-west of the United States of America and in Canada (Hill, 1990). Various other names have been used for the disease; in Germany it is known as xe2x80x9cSeuchenhafter Spxc3xa4tabort der Schweinexe2x80x9d and in North America it is also known as xe2x80x9cMystery Pig Diseasexe2x80x9d, xe2x80x9cMysterious Reproductive Syndromexe2x80x9d, and xe2x80x9cSwine Infertility and Respiratory Syndromexe2x80x9d. In North America, Loula (1990) described the general clinical signs as:
1) off feed, sick animals of all ages;
2) abortions, stillbirths, weak pigs, mummies;
3) post-farrowing respiratory problems; and
4) breeding problems.
No causative agent has as yet been identified, but encephalomyocarditis virus (xe2x80x9cEMCVxe2x80x9d), porcine parvo virus (xe2x80x9cPPVxe2x80x9d), pseudorabies virus (xe2x80x9cPRVxe2x80x9d), swine influenza virus (xe2x80x9cSIVxe2x80x9d), bovine viral diarrhea virus (xe2x80x9cBVDVxe2x80x9d), hog cholera virus (xe2x80x9cHCVxe2x80x9d), porcine entero viruses (xe2x80x9cPEVxe2x80x9d), an influenza-like virus, chlamidiae, leptospirae, have all been named as a possible cause (Loula, 1990; Mengeling and Lager, 1990; among others).
The invention provides a composition of matter comprising isolated Lelystad Agent which is the causative agent of Mystery Swine Disease, the Lelystad Agent essentially corresponding to the isolate Lelystad Agent (CDI-NL-2.91) deposited Jun. 5, 1991 with the Institut Pasteur, Collection Nationale de Cultures De Microorganismes (C.N.C.M.) 25, rue du Docteur Roux, 75724-Paris Cedex 15, France, deposit number I-1102. The words xe2x80x9cessentially correspondingxe2x80x9d refer to variations that occur in nature and to artificial variations of Lelystad Agent, particularly those which still allow detection by techniques like hybridization, PCR and ELISA, using Lelystad Agent-specific materials, such as Lelystad Agent-specific DNA or antibodies.
The composition of matter may comprise live, killed, or attenuated isolated Lelystad Agent; a recombinant vector derived from Lelystad Agent; an isolated part or component of Lelystad Agent; isolated or synthetic protein (poly)peptide, or nucleic acid derived from Lelystad Agent; recombinant nucleic acid which comprises a nucleotide sequence derived from the genome of Lelystad Agent; a (poly)peptide having an amino acid sequence derived from a protein of Lelystad Agent, the (poly)peptide being produced by a cell capable of producing it due to genetic engineering with appropriate recombinant DNA; an isolated or synthetic antibody which specifically recognizes a part or component of Lelystad Agent; or a recombinant vector which contains nucleic acid comprising a nucleotide sequence coding for a protein or antigenic peptide derived from Lelystad Agent.
On the DNA level, the invention specifically provides a recombinant nucleic acid, more specifically recombinant DNA, which comprises a Lelystad Agent-specific nucleotide sequence shown in FIG. 1 (SEQ ID NO: 1) which includes FIGS. 1a; through 1q. Preferably, the Lelystad Agent-specific nucleotide sequence is selected from any one of the ORFs (Open Reading Frames) shown in FIG. 1 (SEQ ID NO: 1).
On the peptide/protein level, the invention specifically provides a peptide comprising a Lelystad Agent-specific amino acid sequence shown in FIG. 1 (SEQ ID NO: 1).
The invention further provides a vaccine composition for vaccinating animals, in particular mammals, more in particular pigs or swine, to protect them against Mystery Swine Disease, comprising Lelystad Agent, either live, killed, or attenuated; or a recombinant vector which contains nucleic acid comprising a nucleotide sequence coding for a protein or antigenic peptide derived from Lelystad Agent; an antigenic part or component of Lelystad Agent; a protein or antigenic polypeptide derived from, or a peptide mimicking an antigenic component of, Lelystad Agent; and a suitable carrier or adjuvant.
The invention also provides a vaccine composition for vaccinating animals, in particular mammals, more in particular pigs or swine, to protect them against a disease caused by a pathogen, comprising a recombinant vector derived from Lelystad Agent, the nucleic acid of the recombinant vector comprising a nucleotide sequence coding for a protein or antigenic peptide derived from the pathogen, and a suitable carrier or adjuvant.
The invention further provides a diagnostic kit for detecting nucleic acid from Lelystad Agent in a sample, in particular a biological sample such as blood or blood serum, sputum, saliva, or tissue, derived from an animal, in particular a mammal, more in particular a pig or swine, comprising a nucleic acid probe or primer which comprises a nucleotide sequence derived from the genome of Lelystad Agent, and suitable detection means of a nucleic acid detection assay.
The invention also provides a diagnostic kit for detecting antigen from Lelystad Agent in a sample, in particular a biological sample such as blood or blood serum, sputum, saliva, or tissue, derived from an animal, in particular a mammal, more in particular a pig or swine, comprising an antibody which specifically recognizes a part or component of Lelystad Agent, and suitable detection means of an antigen detection assay.
The invention also provides a diagnostic kit for detecting an antibody which specifically recognizes Lelystad Agent in a sample, in particular a biological sample such as blood or blood serum, sputum, saliva, or tissue, derived from an animal, in particular a mammal, more in particular a pig or swine, comprising Lelystad Agent; an antigenic part or component of Lelystad Agent; a protein or antigenic polypeptide derived from Lelystad Agent; or a peptide mimicking an antigenic component of Lelystad Agent; and suitable detection means of an antibody detection assay.
The invention also relates to a process for diagnosing whether an animal, in particular a mammal, more in particular a pig or swine, is contaminated with the causative agent of Mystery Swine Disease, comprising preparing a sample, in particular a biological sample such as blood or blood serum, sputum, saliva, or tissue, derived from the animal, and examining whether it contains Lelystad Agent nucleic acid, Lelystad Agent antigen, or antibody specifically recognizing Lelystad Agent, the Lelystad Agent being the causative agent of Mystery Swine Disease and essentially corresponding to the isolate Lelystad Agent (CDI-NL-2.91) deposited 5 Jun. 1991 with the Institut Pasteur, Paris, France, deposit number I-1102.
The invention is a result of combined efforts of the Central Veterinary Institute (CVI) and the Regional Animal Health Services (RAHS) in the Netherlands in trying to find the cause of the new disease MSD. Farms with pigs affected by the new disease were visited by field veterinarians of the RAHS. Sick pigs, specimens of sick pigs, and sow sera taken at the time of the acute and convalescent phase of the disease were sent for virus isolation to the RAHS and the CVI. Paired sera of affected sows were tested for antibodies against ten known pig-viruses. Three different viruses, encephalomyocarditis virus, porcine entero virus type 2, porcine entero virus type 7, and an unknown agent, Lelystad Agent (LA), were isolated. Sows which had reportedly been struck with the disease mainly seroconverted to LA, and rarely to any of the other virus isolates or the known viral pathogens. In order to reproduce MSD experimentally, eight pregnant sows were inoculated intranasally with LA at day 84 of gestation. One sow gave birth to seven dead and four live but very weak piglets at day 109 of gestation; the four live piglets died one day after birth. Another sow gave birth at day 116 to three mummified fetuses, six dead piglets and three live piglets; two of the live piglets died within one day. A third sow gave birth at day 117 to two mummified fetuses, eight dead and seven live piglets. The other sows farrowed around day 115 and had less severe reproductive losses. The mean number of live piglets from all eight sows at birth was 7.3 and the mean number of dead piglets at birth was 4.6. Antibodies directed against LA were detected in 10 out of 42 serum samples collected before the pigs had sucked. LA was isolated from three piglets that died shortly after birth. These results justify the conclusion that LA is the causal agent of mystery swine disease.
LA grows with a cytopathic affect in pig lung macrophages and can be identified by staining in an immuno-peroxidase-monolayer assay (IPMA) with post-infection sera of pigs c 829 and b 822, or with any of the other post-infection sera of the SPF pigs listed in table 5. Antibodies to LA can be identified by indirect staining procedures in IPMA. LA did not grow in any other cell system tested. LA was not neutralized by homologous sera, or by sera directed against a set of known viruses (Table 3). LA did not haemagglutinate with the red blood cells tested. LA is smaller then 200 nm since it passes through a filter with pores of this size. LA is sensitive to chloroform. The above results show that Lelystad Agent is not yet identified as belonging to a certain virus group or other microbiological species. It has been deposited 5 Jun. 1991 under number I-1102 at Institute Pasteur, France.
The genome organization, nucleotide sequences, and polypeptides derived therefrom, of LA have now been found. These data together with those of others (see below) justify classification of LA (hereafter also called Lelystad Virus or LV) as a member of a new virus family, the Arteriviridae. As prototype virus of this new family we propose Equine Arteritis Virus (EAV), the first member of the new family of which data regarding the replication strategy of the genome and genome organization became available (de Vries et al., 1990, and references therein). On the basis of a comparison of our sequence data with those available for Lactate Dehydrogenase-Elevating Virus (LDV; Godeny et al., 1990), we propose that LDV is also a member of the Arteriviridae.
Given the genome organization and translation strategy of Arteriviridae, it seems appropriate to place this new virus family into the superfamily of coronaviruses (Snijder et al., 1990a).
Arteriviruses have in common that their primary target cells in respective hosts are macrophages. Replication of LDV has been shown to be restricted to macrophages in its host, the mouse; whereas this strict propensity for macrophages has not been resolved yet for EAV and LV.
Arteriviruses are spherical enveloped particles having a diameter of 45-60 nm and containing an icosahedral nucleocapsid (Brinton-Darnell and Plagemann, 1975; Horzinek et al., 1971; Hyllseth, 1973).
The genome of Arteriviridae consists of a positive stranded polyadenylated RNA molecule with a size of about 12-13 kilobases (kb) (Brinton-Darnell and Plageman, 1975; van der Zeijst et al., 1975). EAV replicates via a 3xe2x80x2 nested set of six subgenomic mRNAs, ranging in size from 0.8 to 3.6 kb, which are composed of a leader sequence, derived from the 5xe2x80x2 end of the genomic RNA, which is joined to the 3xe2x80x2 terminal body sequences (de Vries et al., 1990).
Here we show that the genome organization and replication strategy of LV is similar to that of EAV, coronaviruses and toroviruses, whereas the genome sizes of the latter viruses are completely different from those of LV and EAV.
The genome of LV consists of a genomic RNA molecule of about 14.5 to 15.5 kb in length (estimated on a neutral agarose gel), which replicates via a 3xe2x80x2 nested set of subgenomic RNAs. The subgenomic RNAs consist of a leader sequence, the length of which is yet unknown, which is derived from the 5xe2x80x2 end of the genomic RNA and which is fused to the body sequences derived from the 3xe2x80x2 end of the genomic RNA (FIG. 2).
The nucleotide sequence of the genomic RNA of LV was determined from overlapping cDNA clones. A consecutive sequence of 15,088 bp was obtained covering nearly the complete genome of LV (FIG. 1, SEQ ID NO: 1). In this sequence 8 open reading frames (ORFs) were identified: ORF 1A, ORF 1B, and ORFs 2 to 7.
ORF 1A and ORF 1B are predicted to encode the viral replicase or polymerase (SEQ ID NO: 2 and SEQ ID NO: 3), whereas ORFs 2 to 6 are predicted to encode structural viral membrane (envelope) associated proteins (SEQ ID NOS: 4-8). ORF 7 is predicted to encode the structural viral nucleocapsid protein (SEQ ID NO: 9).
Because the products of ORF 6 and ORF 7 of LV (SEQ ID NO: 8 and SEQ ID NO: 9) show a significant similarity with VpX and Vp1 of LDV, respectively, it is predicted that the sequences of ORFs 6 and 7 will also be highly conserved among antigenic variants of LV.
The complete nucleotide sequence of FIG. 1 (SEQ ID NO: 1) and all the sequences and protein products encoded by ORFs 1 to 7 (SEQ ID NOS: 1-9) and possible other ORFs located in the sequence of FIG. 1 (SEQ ID NO: 1) are especially suited for vaccine development, in whatever sense, and for the development of diagnostic tools, in whatever sense. All possible modes are well known to persons skilled in the art.
Since it is now possible to unambiguously identify LA, the causal agent of MSD, it can now be tested whether pigs are infected with LA or not. Such diagnostic tests have, until now, been unavailable.
The test can be performed by virus isolation in macrophages, or other cell culture systems in which LA might grow, and staining the infected cultures with antibodies directed against LA (such as post-infection sera c 829 or b 822), but it is also feasible to develop and employ other types of diagnostic tests.
For instance, it is possible to use direct or indirect immunohistological staining techniques, i.e., with antibodies directed to LA that are labeled with fluorescent compounds such as isothiocyanate, or labeled with enzymes such as horseradish peroxidase. These techniques can be used to detect LA antigen in tissue sections or other samples from pigs suspected to have MSD. The antibodies needed for these tests can be c 829 or b 822 or other polyclonal antibodies directed against LA, but monoclonal antibodies directed against LA can also be used.
Furthermore, since the nature and organization of the genome of LA and the nucleotide sequence of this genome have been determined, LA-specific nucleotide sequences can be identified and used to develop oligonucleotide sequences that can be used as probes or primers in diagnostic techniques such as hybridization, polymerase chain reaction, or any other techniques that are developed to specifically detect nucleotide acid sequences.
It is also possible to test for antibodies directed against LA. Table 5 shows that experimentally infected pigs rapidly develop antibodies against LA, and table 4 shows that pigs in the field also have strong antibody responses against LA. Thus, it can now also be determined whether pigs have been infected with LA in the past. Such testing is of utmost importance in determining whether pigs or pig herds or pig populations or pigs in whole regions or countries are free of LA. The test can be done by using the IPMA as described, but it is also feasible to develop and employ other types of diagnostic tests for the detection of antibodies directed against LA.
LA-specific proteins, polypeptides, and peptides, or peptide sequences mimicking antigenic components of LA, can be used in such tests. Such proteins can be derived from the LA itself, but it is also possible to make such proteins by recombinant DNA or peptide synthesis techniques. These tests can use specific polyclonal and/or monoclonal antibodies directed against LA or specific components of LA, and/or use cell systems infected with LA or cell systems expressing LA antigen. The antibodies can be used, for example, as a means for immobilizing the LA antigen (a solid surface is coated with the antibody whereafter the LA antigen is bound by the antibody) which leads to a higher specificity of the test, or can be used in a competitive assay (labeled antibody and unknown antibody in the sample compete for available LA antigen).
Furthermore, the above described diagnostic possibilities can be applied to test whether other animals, such as mammals, birds, insects or fish, or plants, or other living creatures, can be, or are, or have been infected with LA or related agents.
Since LA has now been identified as the causal agent of MSD, it is possible to make a vaccine to protect pigs against this disease. Such a vaccine can simply be made by growing LA in pig lung macrophage cultures, or in other cell systems in which LA grows. LA can then be purified or not, and killed by established techniques, such as inactivation with formaline or ultra-violet light. The inactivated LA can then be combined with adjuvantia, such as Freund""s adjuvans or aluminum hydroxide or others, and this composition can then be injected in pigs.
Dead vaccines can also be made with LA protein preparations derived from LA infected cultures, or derived from cell systems expressing specifically LA protein through DNA recombinant techniques. Such subunits of LA would then be treated as above, and this would result in a subunit vaccine.
Vaccines using even smaller components of LA, such as polypeptides, peptides, or peptides mimicking antigenic components of LA, are also feasible for use as dead vaccine.
Dead vaccines against MSD can also be made by recombinant DNA techniques through which the genome of LA, or parts thereof, is incorporated in vector systems such as vaccinia virus, herpesvirus, pseudorabies virus, adeno virus, baculo virus or other suitable vector systems that can so express LA antigen in appropriate cells systems. LA antigen from these systems can then be used to develop a vaccine as above, and pigs, vaccinated with such products would develop protective immune responses against LA.
Vaccines against MSD can also be based on live preparations of LA. Since only young piglets and pregnant sows seem to be seriously affected by infection with LA, it is possible to use unattenuated LA, grown in pig lung macrophages, as vaccine for older piglets, or breeding gilts. In this way, sows can be protected against MSD before they get pregnant, which results in protection against abortions and stillbirth, and against congenital infections of piglets. Also the maternal antibody that these vaccinated sows give to their offspring would protect their offspring against the disease.
Attenuated vaccines (modified-live-vaccines) against MSD can be made by serially passaging LA in pig lung macrophages, in lung macrophages of other species, or in other cell systems, or in other animals, such as rabbits, until it has lost its pathogenicity.
Live vaccines against MSD can also be made by recombinant DNA techniques through which the genome of LA, or parts thereof, is incorporated in vector systems such as vaccinia virus, herpesvirus, pseudorabies virus, adeno virus or other suitable vector systems that can so express LA antigen. Pigs vaccinated with such live vector systems would then develop protective immune responses against LA.
Lelystad Agent itself would be specifically suited to use as a live vector system. Foreign genes could be inserted in the genome of LA and could be expressing the corresponding protein during the infection of the macrophages. This cell, which is an antigen-presenting cell, would process the foreign antigen and present it to B-lymphocytes and T-lymphocytes which will respond with the appropriate immune response.
Since LA seems to be very cell specific and possibly also very species specific, this vector system might be a very safe system, which does not harm other cells or species.